The invention relates to an electrode component group for a corrosion measuring system for detecting corrosion in a metal embedded in a component made of an ion-conducting material, especially concrete.
Such ion-conducting materials, used for making components in which the electrode component group is used, are especially mineral construction components such as mortar, cement, concrete etc. Steel parts embedded in concrete, such as profiled steel supports or reinforcement inserts of construction steel, in general, are permanently protected against corrosion when the concrete construction component has been processed properly because it is protected under a sufficiently thick concrete cover. This corrosion protection is not based on the impermeability of the concrete to liquids, but resides in the alkalinity of the concrete pore water which is, in general, of a pH value of greater than 12.5. Under these conditions, on the steel surface a thin fixedly attached oxide layer will form which practically completely prevents corrosion. Accordingly, the steel reinforced concrete can be used for external construction components exposed to the elements.
Under unfavorable conditions, especially in the case of faulty construction and especially in salt-containing environmental conditions, the corrosion protection relative to the reinforcements can be lost. The reason for this may be carbonate formation of the concrete which occurs when carbon dioxide contained in the air reacts with alkaline components of the cement. As a result of this, the pH value will decrease so that no corrosion protection is present anymore. Another cause for corrosion is the penetration of chlorides into the concrete which may occur when the concrete component is used, for example, as a street surface or is in the vicinity of a street surface onto which de-icing salt has been dispensed. Such de-icing salt contains, in general, salt derived from sea water or chloride-containing salts of other origins. Both processes begin at the surface of the concrete and extend into the exterior of the concrete to the steel parts embedded therein where their oxide layer begins to dissolve. At the steel surface a critical state of increasing corrosion will result without this being noticeble at the concrete surface. The corrosion damage is, in general, only then recognized when the corrosion of the steel has progressed and the pressure of the rust products causes the concrete layer to chip off.
From EP 0 364 841 B1 a corrosion measuring system for determining corrosion of steel embedded in concrete construction components is known which comprises a multiple anode electrodes arranged spaced apart from one another within the concrete construction component and comprised of regular construction steel. They are arranged at different depths in the concrete construction component and are electrically connected to at least one cathode electrode by a measuring circuit accessible from the exterior, whereby the cathode electrode is comprised of a more noble material. By electrically connecting one of the anode electrodes with the cathode electrode, the corrosion state of the respective anode electrode and thus the progress of corrosion in the concrete construction component can be determined. In the known corrosion measuring system, it is necessary to integrate the individual anode electrode and cathode electrodes during manufacture of the concrete construction component which does not allow for subsequent corrosion testing of concrete construction components which have not been provided initially with such a corrosion measuring system.
From U.S. Pat. No. 2,947,679 an arrangement for determining the corrosion rate of different materials is known. At the outer surface of a tubular support member electrode rings of the materials to be tested are arranged spaced to one another. At one end of the tubular support member, comprised of insulating material, a reference electrode is arranged. All electrodes are provided with lines which are guided through the interior of the tubular support member and are connectable to a measuring circuit. The entire arrangement can be inserted into a bath containing a corroding liquid, for example, an acidic aqueous solution. By electrically connecting the different measuring electrodes to the reference electrode, the different corrosion of the measuring electrodes can be determined. An introduction of this system directly into a concrete construction component is not envisioned.
It is an object of the invention to provide an electrode component group for a corrosion measuring system for determining corrosion of a metal embedded in a concrete construction component which electrode component group can be retrofitted in a simple manner into a concrete construction component whose corrosion is to be measured.